William Gaillard, a special adviser to Platini, told The Associated Press the head of European soccer's governing body fainted, but initial tests at the hospital showed his condition was not serious.
Gaillard said from London that Platini has had flulike symptoms and a mild fever for a few days.
In a statement, UEFA said Platini was taken to the hospital as a precaution.
"Contrary to some media reports, no signs of any heart-related problems have been found and Mr. Platini will be kept overnight for observation as a precautionary measure," the statement said.
Platini was at a restaurant in the Michelangelo Towers mall, attached to FIFA's designated hotel.
Platini is a member of FIFA's executive committee and World Cup organizing committee, and is in Johannesburg for Sunday's final.
Platini, who has led UEFA since 2007, led France to the World Cup semifinals in 1982 and 1986.